An internal resonator type SHG light source has been widely used for its beneficial features of high electro-optic conversion efficiency, low power consumption, and producing green laser light, which is very difficult to be produced as a laser light from a semiconductor laser.
FIG. 9 shows a schematic structure of an internal resonator type SHG light source 100 shown in patent document 1 as a conventional example of this type of the SHG light source. In the conventional SHG light source, a pump light 117 emitted from a semiconductor laser 101 is focused on a solid-state laser 103 by a lens 102. A fundamental wave 118 excited by the pump light is emitted from the solid-state laser 103 and the fundamental wave 118 resonates in a resonator formed by a reflecting surface formed on the solid-state laser 103 and a reflecting surface of an output mirror 106, thereby generating laser oscillation. In the resonator, a quasi phase matching wavelength conversion element 104 is provided to wavelength convert the fundamental wave 118 into a second harmonic 119. Furthermore, an etalon 105 is provided in the resonator to reduce the noise of the resonator. The semiconductor laser 101 and the quasi phase matching wavelength conversion element 104 are respectively temperature controlled by holders 107, 108, Peltier elements 109, 110 and a temperature controller 115. An output of the second harmonic 119 has a part thereof branched off by a splitter 111 to be monitored by a detector 112, and the output stabilization of the second harmonic 119 is realized by a comparator 113 and a drive controller 114.
In patent document 1, the quasi phase matching wavelength conversion element 104 is rotated using a helical coil 116 to compensate for a manufacturing variation of a polarization reversal region formed in the quasi phase matching wavelength conversion element 104 for phase matching.
However, in the conventional internal resonator type SHG light source, the output of the light source is stabilized using a plurality of Peltier elements as described above. The use of such Peltier elements; however, causes problems including an increase in power consumption, higher cost, heat generation of the Peltier elements and the enlargement of a light source device by the Peltier elements. These problems are serious in the applications of the consumer products.
Patent Document 1:
Japanese Unexamined Patent Publication No. 2003-174222.